validation.scala

import shapeless._
import poly._
import syntax.std.tuple._

type Va[+A] = Validation[String, A]
type Vali[+A, -B] = Kleisli[Va, A, B]
def Vali[A, B](fn: A => Va[B]): Vali[A, B] = Kleisli[Va, A, B](fn)

implicit val vaBinding = new Bind[Va] {
  def map[A, B](fa: Va[A])(f: A => B): Va[B] = fa.map(f)
  def bind[A, B](fa: Va[A])(f: A => Va[B]): Va[B] = fa.flatMap(f)
}

def nonEmpty[A] = (msg: String) => Vali { a: Option[A] =>
  a.toSuccess(msg)
}

def validIso2CountryCode = (msg: String) => Vali { x: String =>
  IsoCountryCodes2to3.get(x).toSuccess(msg)
}

val postalCode: Option[String] = request.param[String]("postalcode", allowEmpty = false)
val countryCode: Option[String] = request.param[String]("countrycode", allowEmpty = false)

val b = (
  postalCode |> nonEmpty[String]("postal code missing"),
  countryCode |> nonEmpty[String]("country code missing") >=> validIso2CountryCode("country code invalid")
)

b.map(_.toValidationNel).reduce(_ |@| _)